The malleability of neuronal circuits by environmental conditions is a crucial property in developing brain in fostering adaptive development of perceptual and behavioral faculties. This is particularly obvious in sensory systems, and brainstem taste pathway is potentially a suitable model system to understand competitive interactions and activity dependent reorganization, two possible mechanisms of neuronal malleability, also termed plasticity. Understanding the mechanisms of plasticity is a major step in developing strategies to avoid developmental defects, and to foster normal development of the brain function. A research program is designed to determine whether taste circuits have cellular and molecular components that may allow sensory systems to undergo changes during perturbation of the normal environmental stimuli. The first study aims to obtain evidence for whether distinct gustatory nerves converge upon individual neurons. The technique that will be utilized is a combination of anterograde and retrograde tract- tracing anatomy, high-resolution confocal microscopy using three different fluorophores and 3-dimentional electron microscopy. How and when in development such input convergences occur will have important outcomes for our understanding of the role of competitive interactions in plasticity. The second and the third aims of the proposed project will build upon our existing knowledge of fine synaptic structure of gustatory brainstem, and characterize glutamatergic inputs and their contribution to neuronal circuits. Specifically, pre- and post-synaptic morphological interactions, specificity of different glutamate receptors to afferent and feedback inputs, and developmental changes in NMDA type glutamate receptors at gustatory afferents will be studied. The potential findings of the proposed experiments shall provide novel information on target selectivity of two gustatory nerves, as well as underlining gustatory afferent development as a model to study developmental plasticity and lifelong synaptic stability. PUBLIC HEALTH RELEVANCE: Sensory and dietary circumstances in early development greatly influence developing brain, leading to lifelong changes in brain structure and function, and to deficits of sensory communication. Understanding the mechanisms that render developing pathways vulnerable to environment is a major step in developing strategies to avoid developmental defects, and to foster normal development of the brain function.